C.—GEOLOGY 63 
Marine Bands in Yorkshire and Nottinghamshire similarly wedge out 
rapidly towards the east and south. Across Lancashire the westward 
diminution of thickness is continuous. About Oldham the Dukinfield 
Marine Band is 1,250 ft. above the Furnace Coal, whereas at Tyldesley 
its place is less than 800 ft. above the Rams. In the trough of North 
Staffordshire near Tunstall the Speedwell Marine Band is 1,400 ft. 
above the Ten Foot Coal, but there is rapid wedging out of measures 
both towards the western anticline and towards the south. 
The Pottery Marl and Blackband Ironstone series of the A. Phillipsii 
zone in North Staffordshire may be 1,200 ft. thick. They pass up into 
an equal or greater thickness of red and mottled Etruria Marls. In 
South-east Lancashire 1,800 ft. of grey measures, including the Bradford 
group of coals, overlie the Worsley Four Foot (which may be the Shafton 
Coal of Yorkshire), and underlie the variegated marls and limestones of 
the Ardwick series. East of the Pennines Etruria Marls are preserved 
only in the centres of the synclines. Beneath them in South Yorkshire, 
above the Shafton Marine Band, grey beds, mostly sandstones, are 
1,200 ft. thick, but between Mansfield and Nottingham equivalent 
measures thin south-eastwards to less than 300 ft. 
Because of cumulative displacement by negative pulsations, and 
because the supply of sediment was never-failing, Coal Measures in the 
great coalfields which flank the southern Pennines are an expanded series. 
Southwards along the margins of the Province less accommodation was 
provided, and Productive Measures taper out against the Midland barrier 
of St. George’s Land. Zonal correlation by non-marine lamellibranchs is 
not yet available for the Thick Coal district of South Staffordshire and 
Warwick, and the best suggestion for correlation of horizons is by the tracing 
of coal seams in relation to occasional marine bands. Away from the 
Pennines, the G. or Alton Marine Band has not been proved beyond South 
Derbyshire, where it lies about 1,000 ft. below the Main Coal, and has 
below it Millstone Grit. A more persistent marine band overlies the 
Main Coal in Leicestershire and the Seven Foot Coal in Warwickshire, 
and this may be the White Stone Band below the Heathen Coal of the 
Black Country and the Pennystone of Coalbrookdale. If one may guess 
that it is also the Speedwell Band of Staffordshire, its position within 
_ 200 or even 100 ft. above the pre-Carboniferous bed-rock of the Thick 
Coal districts is evidence that these shores of the Midland barrier did not 
come within the belt of sedimentation until a late stage of the infilling of 
the Coal Measure basin. If it represents the marine band above the 
Seven Foot Banbury, at the base of the Modiolaris zone, it must indicate 
that the creeping transgression which brought these beds across the 
upraised edges of Midland Visean and Lancastrian deposits was in- 
ordinately slow. The thickness of the Productive Coal Measure sedi- 
ments accommodated in the Midland coalfields is from one-tenth to one- 
fifth of that disposed in the Central Pennine area of North Staffordshire. 
Conditions must have been strangely static for a very long period when 
the Thick Coals were growing, but within that series there are no more 
appearances of stratigraphical discordance than where equivalent sedi- 
ments are thick. 
